It's my understanding (via stevebarr, who is/was sufficiently dialed in to The Industry for me to give this credence) that the creative team had already done a treatment when they discovered the similarities to the novel, so they bought the rights to cover their legal liabilities.

Personally, I'm stupidly excited about this, not simply because I loved the book, but because Powers is Author Guest of Honor at the Reno WorldCon not quite three months after the movie is slated for release, so I'm seeing the potential for all kinds of goodies at the convention.